Dwarf Planet

REFERENCE MATERIAL ABOUT DWARF PLANETS

Dwarf planets are a new category of solar system bodies created by the International Astronomical Union in 2006. Confusingly, dwarf planets are not a subset of planets, but a separate group. The official I.A.U. definition states: A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

At present, there are three recognized dwarf planets in the solar system: Pluto, the asteroid Ceres and Xena (more technically designated 2003 UB313), a Kuiper Belt object discovered in 2005 that is slightly larger than Pluto. However, planetary scientists believe that most objects wider than 500 miles have enough gravitational pull to become round. About 40 other known solar system bodies are larger than this size, and they may be added to the roster of dwarf planets. Astronomers also expect that many more dwarf planets will be discovered in the Kuiper Belt in the coming years.